The origin of plants: genomes, rocks, and biochemical cycles

There can be no doubt that early land plant evolution transformed the planet but how our knowledge of how this happened is in disarray. The clear coincidence in the first appearance of land plant fossils and formative shifts in atmospheric oxygen and CO2 is an artefact of the absence of earlier terrestrial rocks, and disentangling the timing of land plant bodyplan assembly and its impact on global biogeochemical cycles requires a new understanding of early land plant evolution and the timescale over which it was effected.

Early life on land was mostly microbial, but sometime between about 700 million and 420 million years ago plants moved from water onto land. The timeframe is controversial and as currently understood it is very broad, but a more precise knowledge of the events is key to linking the early evolution of plant life to major environmental change. Ambiguity and uncertainty arise because the principal lines of evidence conflict. Fossils, notably plant microfossils (spores), point to colonization beginning about 470 Ma (million years ago), but the affinities of the early spore producers are controversial. Macrofossils (plant stems, multicellular organ systems, etc) indicate a later colonization, beginning about 430 Ma. Calibrated molecular phylogenies - studies of the timing of divergence of living plant lineages based on molecular sequence data, where the rate of mutation is calibrated to time using fossils - point to an origin and early evolution of life on land that may have begun during the Late Neoproterozoic, long predating the fossil evidence. Recent research has identified difficulties with both molecular phylogenetic and palaeontological approaches, which our proposed research program will address.

We have assembled a multidisciplinary team to conduct research to remedy these shortcomings. We will establish a robust genealogy for living plant lineages based on a genome-scale amount of molecular sequence data (~1,000s genes and, therefore, ~1,000,000s nucleotides). The genealogy will be linked to time by including important and exceptionally preserved fossil species. These will be correctly placed through detailed characterization of their anatomy using state of the art Synchrotron Computed Tomography, a novel approach that we have recently shown to provide valuable new data in a recent proof of concept study. Sedimentary regime is known to affect the age estimate given by fossils, so we will also apply new methods develop by us to assess and to correct for this. Together, these approaches will enable us to develop a robust phylogeny calibrated with greater precision to time, which we will use to investigate the evolutionary assembly of key land plant organs and tissue systems (e.g., roots, stomata, vascular tissue, leaves) and their impact on major biogeochemical cycles. Finally, we will we will explore the implications of our plant evolutionary timescale within a leading computer model of global biogeochemical cycling (GENIE). This will enable us to generate predictions for levels of atmospheric carbon dioxide levels and of organic carbon productivity that we will test against geological observations. Ultimately, we will establish a new scenario for the timing and tempo of early land plant evolution, the assembly of land plant bodyplans, and a new understanding of the effect of this episode upon the evolution of the Earth System.

museum visitors, and the amateur naturalist community. We will reach these diverse audiences through a combination of tailored standard academic practices and innovative means of communication led by experts in science communication at one of our major national museums. The process and results of our research will significantly enhance The Natural History Museum's Science Communication Programme, providing direct educational benefits to secondary school students and cultural benefits to the general public.

Because of the subject matter and the multidisciplinary nature of the proposed research, our results will be of interest to a diverse scientific audience, including both Life Scientists (systematic botanists, molecular systematists, evolutionary and developmental biologists) and Earth Scientists (palaeobotanists, micropalaeontologists, sedimentary geologists, geochemists). The results, novel data and methods in our Time Tree project are relevant to the former, whereas the latter will be most interested in our analyses of the Rock Record. Both groups as well as (palaeo-)climatologists will be interested in the synthesis, which is concerned with how the geochemical carbon cycle is best calibrated in light of a revised time scale for key events in land plant evolution (e.g., rates of carbon sequestration, weathering of surface rocks, soil development). New datasets will be made publicly available via the TimeTree project, DRYAD, TreeBASE and The Paleobiology Database. Results will be disseminated through the scientific press and at scientific meetings, and we will target both Earth and Life Science outlets. Major results will be communicated through the press office at all three partner institutions.

Schools and museum visitors are identified as the major wider beneficiaries, because our central question involves a key event in the history of life. The story of the earliest life on land is accessible to students and to the broader public, and it provides a compelling springboard for showing how scientists approach studying evolution as a process and its impact on the natural environment. Schools and public engagement are therefore a major focus of our Impact Plan. We will draw on expertise in science communication, facilities, and the current diverse programme plan in place at The Natural History Museum. We will be working directly with learning professionals who engage with policy makers on schools policy and UK government public engagement policy.

The Natural History Museum attracts some 150,000 school visitors each year, 25% of whom participate in formal activities. Under the guidance of professional science educators, we (Investigators, PDRAs) will contribute to curriculum linked activities already in place such as "How Science Works", "Science Focus", "A-level Biology Days", and the "Earth Science Fair" for science teachers and school children. PDRAs will participate in the Research Councils' "Researcher in Residence" school program to reinforce their science communication skills developed in the museum and to bring real working science into the classroom. School children will have the opportunity to contribute directly to our data by collecting plants in the UK, which will be used in molecular labwork.
Museum public and amateur naturalists will be engaged in several ways. We will communicate (onsite and remotely via webcam) through our "Nature Live" series presentations at The Natural History Museum and through our Angela Marmont Centre for UK Biodiversity, which plays a key role in supporting networks of societies and other partners working in the field of natural history across the UK.